1. Technical Field
The present invention relates to a mounting structure of a circuit board having a multi-layered ceramic capacitor thereon, and more particularly, to a mounting structure of a circuit board having a multi-layered ceramic capacitor thereon, which makes a coating height of a solder lower than a height of a cover layer when horizontally mounting the multi-layered ceramic capacitor on the circuit board, thereby reducing vibration noise of the multi-layered ceramic capacitor.
2. Description of the Related Art
In general, a multi-layered ceramic capacitor (MLCC) is a chip type condenser that is mounted on a printed circuit board of diverse electronic products such as mobile communication terminals, laptop computers, computers, and personal mobile terminals (PDA) to perform a main function such as charging or discharging electricity, and adopts various sizes and layering patterns according to its purpose and capacitance.
Also, the multi-layered ceramic capacitor has a structure in which internal electrodes of a different polarity are alternately layered between a plurality of dielectric layers.
Such a multi-layered ceramic capacitor has been widely used as a part for diverse electronic devices because of its advantages of being miniaturized, while guaranteeing high capacitance, and being easily mounted.
As a ceramic material for forming a layered unit of the multi-layered ceramic capacitor, a ferroelectric material such as Barium Titanate with relatively high permittivity is generally used. However, since the ferroelectric material has piezoelectricity and electrostriction, stress and mechanical deformation appear as vibration when an electric field is applied to the ferroelectric material, and the vibration is transmitted to the board from a terminal electrode of the multi-layered ceramic capacitor.
That is, if an alternating current (AC) voltage is applied to the multi-layered ceramic capacitor, stresses (Fx, Ft, and Fz) are generated in directions of X, Y, and Z in an element body of the multi-layered ceramic capacitor, and vibration is generated due to the stresses. The vibration is transmitted to the board from the terminal electrode and thus the whole board becomes an acoustic radiation surface, generating vibrating sound as noise.
Most of the vibrating sound corresponds to vibrating sound of an auditory frequency (20˜20000 Hz) and may have a compass unpleasant to people. Therefore, a solution to this problem is demanded.
Recently, in order to solve the problem caused by the vibrating sound, various techniques, such as a technique of preventing vibration by means of elastic deformation of an external terminal of the multi-layered ceramic capacitor, a technique of adopting a separate part to prevent noise by suppressing radio wave of vibration caused by piezoelectricity and electrostriction, and a technique of forming a board hole around the mounted multi-layered ceramic capacitor in order to suppress vibration of the board, have been suggested. However, these techniques require a separate process and do not obtain a remarkable vibration preventing effect for the complicated process.
The multi-layered ceramic capacitor may have substantially the same width and thickness. In the case of the multi-layered ceramic capacitor with substantially the same width and thickness, when the multi-layered ceramic capacitor is mounted on the printed circuit board, it is difficult to recognize directivities of internal conductors of the multi-layered ceramic capacitor by external appearances of the multi-layered ceramic capacitor. Therefore, the multi-layered ceramic capacitor is mounted on the printed circuit board regardless of the directivities of the internal conductors.
According to the directions of the internal conductors of the multi-layered ceramic capacitor mounted on the printed circuit board, there is a difference in the characteristics of the multi-layered ceramic capacitor, and in particular, there is a big difference in the vibration noise characteristic by the piezoelectricity of the multi-layered ceramic capacitor.
According to a recent experimental result, a mounting direction of the multi-layered ceramic capacitor correlates an amount of conductive material that connects an external terminal electrode of the multi-layered ceramic capacitor to a land, and the mounting direction of the multi-layered ceramic capacitor and the amount of conductive material greatly affects the vibration noise characteristic.
Particularly, since it is possible to noticeably reduce the vibration noise of the multi-layered ceramic capacitor by mounting the multi-layered ceramic capacitor with its internal electrode surface being in parallel to the surface of the printed circuit board and by adjusting a ratio between a bonding height of the conductive material to connect the external terminal electrode to the land and a bonding height of the external terminal electrode, there is a demand for a mounting structure to reduce vibration noise.